Thin film magnetic recording disks generally comprise a disk substrate having a magnetic layer and a number of underlayers and overlayers deposited thereon. The nature and composition of each layer is selected to provide desired magnetic recording characteristics, as generally recognized in the industry. An exemplary present day thin film disk comprises a non-magnetic disk substrate, typically composed of an aluminum alloy. An amorphous nickel phosphorous (Ni—P) underlayer is formed over each surface of the disk substrate, typically by plating and is subsequently polished and sometimes texturized prior to deposition of the additional films. The Ni—P layer is hard, and imparts rigidity to the aluminum substrate. Alternatively, glass and other non-metallic materials are now used to form highly rigid disk substrates. A second underlayer in the form of a chromium ground layer is formed over the Ni—P layer, typically by sputtering, and a magnetic layer is formed over the ground layer. The magnetic layer comprises a thin film of ferromagnetic material, such as a magnetic oxide or magnetic metal alloy. Usually, a protective layer, such as a carbon film, is formed over the magnetic layer and a lubricating layer is formed over the protective layer.
The presence of the Ni—P underlayer, together with the chromium ground layer, has been found to improve the recording characteristics of the magnetic layer. In particular, the chromium ground layer formed over a Ni—P layer provides enhanced coercivity and reduced noise characteristics. Such improvements are sometimes further enhanced when the Ni—P underlayer is treated by mechanical texturing to create a roughened surface prior to formation of the chromium ground layer. The texturing may be circumferential or crosswise, with the preferred geometry depending on the particular composition of the cobalt-containing magnetic layer.
The outer carbon protective layer serves a very different purpose. This protective layer has been found to greatly extend the life of magnetic recording media by reducing disk wear. Carbon has been shown to provide a high degree of wear protection when a thin lubrication layer is subsequently, applied.
Such magnetic recording disk constructions have been very successful and allow for high recording densities. As with all successes, however, it is presently desired to provide magnetic recording disks having even higher recording densities. One method for increasing the areal density on rigid magnetic disks involves patterning the surface of a thin film disk to form discrete data tracks. Such “discrete track media” typically include surface geometry data which are utilized by the hard disk drive servo mechanism, allowing specific recording tracks to be identified, and providing feedback to improve the accuracy of read/write head tracking.
The production of discrete track media and other magnetic recording media having patterned surfaces were described by S. E. Lambert et al. in Beyond Discrete Tracks: Other Aspects of Patterned Media, JOURNAL OF APPLIED PHYSICS, Vol. 69, 8:4724-26, Apr. 15, 1991. Each of the patterned media described were produced by sputter etching or ion milling a magnetic recording layer through a resist mask. The resist mask was written with an electron beam, as is known in the lithographic arts.
The production of discrete track media with a pre-embossed rigid magnetic disk was described by D. Dericotte, et al., in Advancements in the Development of Plastic Hard Disks With Pre-embossed Servo Patterns, CORPORATE RESEARCH LABORATORIES, SONY CORPORATION. The disk is produced using an injection molding process between two stamping plates. The plates containing the media surface pattern are produced using lithographical techniques.
Recording media having a selectively laser-textured surface and methods for their production are described in U.S. Pat. Nos. 5,062,021, and 5,108,781, respectively. A laser system for texturing a substrate, Ni—P layer, or a magnetic recording layer is also disclosed.
Discrete track media, however, suffer from their own disadvantages. The surface patterns of discrete track media have generally been imposed using standard lithographic techniques to remove material from the magnetic recording layer or by creating recessed zones or valleys in the substrate prior to deposition of the magnetic material. In the former case, the magnetic recording material is etched or ion milled through a resist mask to leave a system of valleys which are void of magnetic material. In the latter case, the magnetic film, subsequently applied, is spaced far enough away from the recording head that the flux from the head does not sufficiently “write” the magnetic medium. Servo track information can be conveyed by the difference in magnetic flux at the boundary between the elevatored patterns and the valleys. However, the boundary signals have at most 50% of the amplitude of conventionally recorded data. Additionally, fabrication of production quantities of discrete track media has remained problematic, due in part to the expense of the required lithographic processes.
A narrower track width corresponds to a higher areal density. The photo patterning of media helps separate tracks and also helps increase the areal density. However, the track width produced by photo patterning is greatly limited and does not achieve the desired narrow widths.
There is ever growing need for high areal densities. Sensor dimensions are reduced to read and writer small dimension tracks. In addition to the sensor, the magnetic media also plays a key role in enhancing areal densities.
For these reasons, it would be desirable to provide an improved method for producing a discrete track patterned media. It would be particularly desirable if such a method provided the accuracy and reproducibility of lithography, but did not involve multiple process steps or the complex, dedicated tooling required for stamping. It would be best if such a method enhanced the improvements to the magnetic recording characteristics available using the conventional underlayers, magnetic recording layers, and overlayers of high density magnetic recording media.